Curious George

A fountain of material and immaterial information - Things that I spend my days wondering about... and perhaps you have been too? Check out for more curious questions (and answers to them)

Friday, March 27, 2009

Elevators - all you ever wanted to know

This is a rather lengthy posting by Curious George this time, but its a whopper!

It will tell you a whole lot of interesting stuff about the elevator business.

- How high can an an elevator go?
- How many people die annually from elevator deaths and how to they die? (not from the car falling down)
- Does the door-close button actually work in an elevator? (if its a post-90s built elevator, it probably doesn't)
- How many people can comfortably fit in an elevator in Europe/US vs Asia? (No big surprises there)
- Can you really escape through the roof-hatch when a bomb is about to go off, and there is no Keanu Reaves around?
- Can you survive a freefall by jumping up at the very last second?

If you have asked these questions (and obviously you have), then keep reading.

Traction elevators are the ones hanging from ropes (as opposed to dumbwaiters, or mining elevators, or those lifted by hydraulic pumps) are typically borne aloft by six or eight hoist cables, each of which, according to the national elevator-safety code (That´s the US codes obviously- and the code determines all), is capable on its own of supporting the full load of the elevator plus twenty-five per cent more weight. Another line, the governor cable, is connected to a device that detects if the elevator car is descending at a rate twenty-five per cent faster than its maximum designed speed. If that happens, the device trips the safeties, bronze shoes that run along vertical rails in the shaft. These brakes are designed to stop the car quickly, but not so abruptly as to cause injury. They work. This is why free falling is so rare.

People dying in elevators:

An average of twenty-six people die in (or on) elevators in the United States every year, but most of these are people being paid to work on them. That may still seem like a lot, until you consider that that many die in automobiles every five hours. In New York City, home to fifty-eight thousand elevators, there are eleven billion elevator trips a year thirty million every day and yet hardly more than two dozen passengers get banged up enough to seek medical attention.

An estimated two hundred people were killed in elevators at the World Trade Center on September 11 - some probably in free-fall plunges, but many by fire, smoke, or entrapment and subsequent structural collapse. (the counterweight, which aids an elevators rise and slows its descent, is typically forty per cent heavier than an empty car)

How high can an elevator go?

A single elevator can climb no higher than seventeen hundred feet. A hoist rope any longer is too heavy to be practical; at thirty-two hundred feet, it will snap, like a stream of spit in a stairwell. A decade ago, Otis developed a prototype of a conveyance called Odyssey, which could slide out of its shaft and travel on a horizontal track to another shaft, with the help of a linear induction motor. It was scuttled by the 1997 Asian financial crisis.

The tallest building in the world, the Taipei 101 Tower, which has the fastest elevators in the world rising at more than fifty-five feet per second, or about thirty-five miles an hour. The cars are pressurized, to prevent ear damage.

The basics of getting people from Ground level to 48th floor
In elevatoring, as in life, the essential variables are time and space.
There are two basic elevatoring metrics. One is handling capacity: your aim is to carry a certain percentage of the buildings population in five minutes. Thirteen per cent is a good target. The other is the interval, or frequency of service: the average round-trip time of one elevator, divided by the number of elevators. In an American office building, you want the interval to be below thirty seconds, and the average waiting time to be about sixty per cent of that. Any longer, and people get upset. In a residential building or a hotel, the tolerance goes up, but only by ten or twenty seconds. In the nineteen-sixties, many builders cheated a little accepting, say, a thirty-four-second interval, and 11.5 per cent handling capacity and came to regret it. Generally, England is over-elevatored; India is under-elevatored.

A probable stop table applies probability to the vexation that boils up when each passenger presses a button for a different floor. If there are ten people in an elevator that serves ten floors, it will likely make 6.5 stops. Ten people, thirty floors: 9.5 stops. (The table does not account for the exasperating phantom stop, when no one gets on or off.) Other factors are door open and close time, loading and unloading time, acceleration rate, and deceleration rate, which must be swift but gentle. You hear that interfloor traffic kills something to mutter, perhaps, when a co-worker boards the elevator to travel one flight, especially if that co-worker is planning, at days end, to spend half an hour on a StairMaster. Its also disastrous to have a cafeteria on anything but the ground floor, or one floor above or below it, accessible via escalator.

Engineering feats and developments
In 1973, the designers of the World Trade Center introduced the idea of sky lobbies. A sky lobby is like a transfer station: an express takes you there, and then you switch to a local.

The other was the destination dispatch system that the Marriott introduced, a few years ago, becoming the first hotel in North America to do so. You enter your floor number at a central control panel in the lobby and are told which elevator to take. The wait in the lobby may be longer, but the trip is shorter. Also have lights lighting up a bit of time ahead of the elevator actually arriving is used to play with the psychological waiting time. Its like a nod of acknowledgment from a busy bartender.

There is no control panel in the destination dispatch car; the elevator knows where you are going. People tend to find it unnerving to ride in an elevator with no buttons. In most elevators, at least in any built or installed since the early nineties, the door-close button doesn’t work. It is there mainly to make you think it works. (It does work if, say, a fireman needs to take control. But you need a key, and a fire, to do that.) Once you know this, it can be illuminating to watch people compulsively press the door-close button. That the door eventually closes reinforces their belief in the buttons power. Its a little like prayer. Elevator design is rooted in deception to disguise not only the bare fact of the box hanging by ropes but also the tethering of tenants to a system over which they have no command.

Where to stand in an elevator (and how tight can you stack them)

Passengers seem to know instinctively how to arrange themselves in an elevator. Two strangers will gravitate to the back corners, a third will stand by the door, at an isosceles remove, until a fourth comes in, at which point passengers three and four will spread toward the front corners, making room, in the center, for a fifth, and so on, like the dots on a die. With each additional passenger, the bodies shift, slotting into the open spaces. The goal, of course, is to maintain (but not too conspicuously) maximum distance and to counteract unwanted intimacies a code familiar (to half the population) from the urinal bank and (to them and all the rest) from the subway. One should face front. Look up, down, or, if you must, straight ahead. Mirrors compound the unease. Generally, no one should speak a word to anyone else in an elevator. Most people make allowances for the continuation of generic small talk already under way, or, in residential buildings, for neighborly amenities. The orthodox enforcers of silence the elevator Quakers must suffer the moderates or the serial abusers, as they cram in exchanges about the night, the game, the weekend, or the meal.

The concept of the body ellipse is a birds-eye graphic representation of an individuals personal space. Its essentially a shoulder-width oval with a head in the middle. He employed a standard set of near-maximum human dimensions: twenty-four inches wide (at the shoulders) and eighteen inches deep. If you draw a tight oval around this figure, with a little bit of slack to account for body sway, clothing, and squeamishness, you get an area of 2.3 square feet, the body space that was used to determine the capacity of New York City subway cars and U.S. Army vehicles. Fruin defines an area of three square feet or less as the touch zone; seven square feet as the no-touch zone; and ten square feet as the personal-comfort zone. Edward Hall, who pioneered the study of proxemics, called the smallest range less than eighteen inches between people intimate distance, the point at which you can sense another persons odor and temperature - involuntary confrontation and contact at this distance is psychologically disturbing for many persons.

The standard elevator measure is about two square feet per passenger intimate, disturbing. Elevators represent a special circumstance in which pedestrians are willing to submit to closer spacing than they would normally accept, Fruin wrote, without much parsing the question of willingness. The book contains a pair of overhead photographs, part of an experiment conducted by Otis, of elevators loaded to capacity (by design, cabs are nearly impossible to overweight, unless the passengers are extremely tall). In one, a car is full of women, each of whom has 1.5 square feet of space. In the other, there are men as well as women, and each passenger gets 1.8 square feet per person: men are larger, and women, in their presence, try to claim more space, often by crossing their arms.

There´s a higher tolerance in Asia than in the United States for tight rides and long waits. In China, you´ll get twenty-five people in a four-thousand-pound car. Thats unheard of in the US. Otis does about eighty per cent of its business outside the United States, especially in the high-rise boomtowns of the Gulf states and in China. (Prestige aside, the super-tall tower jobs are basically loss leaders for the elevator companies: Very few high-rise jobs are money makers. You give´em away for the maintenance contract.)

Weird Elevator facts:
The escape hatch is always locked. By law, its bolted shut, from the outside. It´s there so that emergency personnel can get in, not so passengers can get out.

Loading up an empty elevator car with discarded Christmas trees, pressing the button for the top floor, then throwing in a match, so that by the time the car reaches the top it is ablaze with heat so intense that the alloy (called babbitt) connecting the cables to the car melts, and the car, a fireball now, plunges into the pit: this practice, apparently popular in New York City housing projects, is inadvisable.

The timed jump:

To the age-old half-serious question of whether a passenger thundering earthward in a runaway elevator should jump in the air just before impact: you cant jump up fast enough to counteract the rate of descent. And how are you supposed to know when to jump? As for an alternative strategy lie flat on the floor he shrugged: Deads dead.



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